The present invention relates to a pump arrangement for supplying cryogenic liquefied gases such as, for example, liquid helium, nitrogen, hydrogen, and neon, and, more particularly, to a liquefied pump system for supplying liquid helium.
A cryogenic liquefied gas pump proposed in, for example, CRYOGENICS, L. B. Dinaburg et al, July 1977, pages 439-440, with the cryogenic liquefied gas pump including a motor disposed at an upper part of a storage tank for accommodating a liquefied gas or a cryostat, and with a driving shaft of the motor, extending into the tank, having an impeller connected at a lower end thereof. In the proposed liquefied gas pump, the motor is at an ambient room temperature and the pump impeller is at a very low temperature thereby resulting in a temperature differential due to a difference in thermal transmission by the driving shaft and a surrounding housing made of stainless steel.
A disadvantage of the above proposed cryogenic liquefied gas pump resides in the fact that the driving shaft is relatively long and, consequently, it is impossible to provide for a high speed rotation. Moreover, the overall construction of the proposed pump is very complicated.
Yet another disadvantage of the proposed liquefied gas pump resides in the fact that the bearings for the impeller are fashioned as ball bearings exposed to very low temperature liquefied gas and lubricated thereby. Consequently, the bearings are subjected to heavy wear thereby considerably shortening the life span thereof resulting in increased maintenance and repair costs as well as an increase in the number of times the pump must be taken off the line.
In, for example, NBSIR 75-816, July 1975, U.S. Department of Commerce, FIG. 1, a liquefied gas pump is proposed which employs a submerged driving motor and a short driving shaft.
However, disadvantages of the last mentioned liquefied gas pump reside in the fact that since the pump is located in a cryogenic region, the ball bearings are subjected to heavy wear with the attendant disadvantages noted above. Moreover, by subjecting the bearings to cryogenic temperatures, the overall realiability of the pump is relatively low and, with the motor disposed in the cryogenic region, the heat generated by the motor causes a thermal loss in the liquefied gas.
In, for example, U.S. Pat. Nos. 3,369,715 and 3,876,120, similar types of liquefied gas pumps submerged in cryogenic regions are proposed and, consequently, suffer from the above noted disadvantages.
The aim underlying the present invention essentially resides in eliminating the above-noted disadvantages of cryogenic liquefied gas pumps so as to provide a highly realiable compact liquefied gas pump.
In accordance with advantageous features of the present invention, a double insulated tank is formed inside a vessel for storing a liquefied gas so as to maintain an interior of the insulated tank at ambient room temperature, with a drive motor and associated bearings being unitarily accommodated in the interior of the insulated tank, and with an impeller of the pump, located in a very low temperature region, being driven by a drive motor.
In accordance with further features of the present invention, the driving shaft, housing, and insulated tank of the pump are cooled by a latent heat of vaporization during a gasification of a liquefied gas and the sensible heat of the gas at a low temperature so as to reduce the heat leakage to a very low temperature region from a room temperature region thereby enhancing the performance of the pump and preventing thermal deformation of the driving shaft and the housing so as to ensure a stable operation and an increase in the overall realiability of the pump.
Advantageously, in accordance with the present invention, a pump housing is provided for accommodating the motor, the bearings, and the drive shaft, with the pump housing being disposed inside the insulating tank and an outer case portion integrally formed at a lower end of the inner insulating tank.
Preferably, in accordance with the present invention, the bearing means are formed as self acting bearing means.
Additionally, in order to cool the liquefied gas pump by the liquefied gas, in accordance with yet further advantageous features of the present invention, a plurality of minute passage means are provided for enabling a flow of liquefied gas along surfaces of the driving shaft and the pump housing, with release apertures being provided for communicating the respective passages with an exterior of the vessel so as to enable the cryogenic liquid to cool the pump.
Advantageously, a regulator is provided at the respective release apertures for individually regulating a flow rate of the gas through the respective passages.
The passages may, in accordance with the present invention, be formed or defined between the driving shaft and a wall of the pump housing and the outer case portion as well as an inner wall of the inner insulating tank.
By virtue of the features of the present invention and, in particular, the provision of the double insulated tank structure, it is possible to maintain a room temperature zone inside of a cryogenic region of the liquefied gas and to readily utilize bearings which may be lubricated. Moreover, since the driving shaft may be shortened due to the relatively short distance between the drive motor and the impeller, the realiability of the pump is enhanced, a high speed rotation is possible, and a construction of the pump can be greatly simplified.
Additionally, with a double insulated tank structure, heat leakage to the cryogenic liquefied gas region can be prevented and vaporization of the liquefied gas can be minimized so that the pump is highly efficient and a stable operation of the pump is ensured.
Furthermore, since the double insulated tank and the pump housing for receiving the pump are, in accordance with the present invention, separately mounted, mainenance of the system is greatly facilitated since such separate mounting enables a simple detachment of the pump.
Additionally, by providing passages for enabling a flow of the liquefied gas, it is possible to conduct the liquefied gas through the passages or gaps between the driving shaft and the inside housing and between the outside housing and the inner insulated tank so as to enable a cooling of the pump.
Furthermore, by a separate or individual adjustment of the gas flow rates by gas release rate regulating means, it is possible to control the cooling so as to conform with the heat leakage of the respective parts thereby more efficiently reducing the heat leakage.
A further advantage of the present invention resides in the fact that the driving shaft, and the inner and outer sides of the housing as well as the inner insulating tank are uniformly cooled so that a positional deviation between the driving shaft and the housing or between the driving shaft and the inner insulating tank attributable to thermal deformation can occur thereby ensuring a stable operation of the cryogenic liquefied gas pumping system.
Additionally, the features of the present invention ensures that heat leakage, which includes heat generated during rotation of the drive motor in addition to heat attributed to conduction from room temperature parts, is minimized thereby also improving the performance of the system.
Accordingly, it is an object of the present invention to provide a cryogenic liquefied gas pumping system which minimizes if not avoids premature wear of the bearings thereof.
Another object of the present invention resides in providing a cryogenic liquefied gas pumping system which is simple in construction and therefore relatively inexpensive to manufacture.
A further object of the present invention resides in providing a cryogenic liquefied gas pumping system which functions realiably under all operating conditions.
Yet another object of the present invention resides in providing a cryogenic liquefied gas pumping system which ensures a highly realiable operation.
These and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, two embodiments in accordance with the present invention.